Astromech.net - Great resource, with galleries, parts run info and much more.

Victor Franco's R2 Blog - One builder documents the entire droid building process, excellent read.

McMaster.com - No relation, but a great place to get harware.

Rockler.com - Home of the Rockler Lazy Susan bearing used in most domes.

Robotcombat.com - Purchased my NPC motor and wheels from them

Budgetrobotics.com - Lots of neat goodies can be found here. I use the double O-Ring wheels for my dome rotation

Vantec.com - Th ultimate speed controllers for your droid!

Fiber Optic Products - Great source for the PSI's and other fiber related goods.

C-3P0 Builders Club - You can't have an R2 without 3P0!

Images and sounds of R2-D2 and C3P0 are the trademarked property of Lucasfilm Ltd.